I think many of you are forgetting that the main advantage of a hybrid is the ability to capture energy that is normally wasted to heat by the friction brakes. This means that while the energy is indirectly coming from petrol, the engine really isn't working that much harder. The weight of the motor and battery really become negligible with the efficiency gains of regen braking.

And while running the AC in a hybrid is still a waste of energy it is more efficient because the car can charge at a more efficient ICE RPM.

I doubt very much the regenerative braking recovery will come anywhere near compensating for the battery mass penalty. Unless of course you drive downhill all the time.